Nicky Hager's new book, called Dirty Politics, reveals an "attack politics" side of the Key Government, he says, with emails showing how closely it works with blogger Cameron Slater.

The book was based on "thousands and thousands" of documents from Slater's computer, Hager said.

"You are not going to believe how bloody awful it is."

Key said through a spokeswoman that the book was a "cynically timed attack" from "a well known left wing conspiracy theorist"."

"It makes all sorts of unfounded allegations and voters will see it for what it is."

While speculation about what Hager might reveal centred on classified documents held by American Edward Snowden, the Hager book transpired to be a sequel to The Hollow Men, released in 2006.

In that book, Hager had explored tactics used by the National Party to fight the 2005 election.

Hager said his new book focused on individuals in the National Government, including Prime Minister John Key, seniorministers and staff in the PM's office.

Hager said he has obtained emails, among them correspondence between Slater and Key staffers.

"The book is based upon a large number of internal communications between the National-aligned blogger Slater and a network of National Party figures," Hager said in a statement.

"The documents are very revealing about Slater and his collaborators, including much that is shocking and distasteful," he said.

"But much more important the documents also cover politicians and Beehive staff, showing the highly co-ordinated National Party attack politics used year-after-year throughout Key's prime ministership."

Among the revelations in the book, Hager said, are that during the 2011 election campaign Slater obtained a database of Labour Party members, emails and donations to attack Labour with.

Also in 2011 the PM's office used its knowledge of secret SIS documents to tip off Slater and arrange an attack on Labour leader Phil Goff, and drafted Official Information Act requests for Slater to use in other attacks.

SLATER'S RESPONSE

Slater recently arrived in Korea but offered a post on his Whale Oil blog for his readers to chat about the book.

"It is of course likely to be a very single-sided affair, and a direct attack on the government to hurt it at election time. What is being framed here is only one side of politics in New Zealand. Hager conveniently appears to avoid what happens on the left.

"But that's ok," Slater wrote. "Nothing changes."

HAGER'S PAST WORKS

Hager's 2002 book about genetically modified corn lobbed a grenade into that election campaign after former prime minister Helen Clark labelled television interviewer John Campbell a "creep" for ambushing her over its claims.